The present invention relates to a developing unit, more particularly, to a developing unit for developing a latent image on a photoconductor in an image forming apparatus such as a copying machine or a printer.
In a copying machine, for example, a reading unit reads information from original, and then a latent image is formed on a photoconductive drum as determined by the read image information. A developing unit is provided in the copying machine for developing the latent image. The developing unit consists mainly of a developing container having a developing roller and an agitating roller therein, and a hopper for supplying toner to the developing container.
Such a developing unit must be drawn out, or detached, from the copying machine body when the toner is supplied to the developing unit, or during maintenance thereof. Conventionally, the developing unit is moved in the direction parallel to the axis of the photoconductor, or in the rear-to-front direction, when the developing unit is attached or detached. However, since the developing unit must be set very close to the photoconductor, the developing unit may hit or scratch the surface of the photoconductor, damaging the surface. In order to guard the photoconductor against damage when the developing unit is attached or detached, the developing unit may be slid upward and downward as the technology described in U.S. Pat. No. 4,702,587 and Japanese Patent Laying-Open No. 214778/1988 discloses.
In the above copying machine, an operator can obtain different color copy by exchanging developing units. However, since the developing unit is large because it comprises a hopper fixed to the developing device, it is cumbersome to exchange developing units. Although the hopper storing toner could be minimized to facilitate the exchanging operation, this would counter current situations, in which copying machines are frequently used and a large amount of copies must be made very quickly.
Usually, copying machines consume black toner to a much greater extent than other toner, such as red. However, in the above conventional units the developing devices and hoppers are fixed together and the volume of each of these hoppers is the same. Therefore, every hopper must be able to accommodate the toner which is consumed most, so that the developing units must be unnecessarily large.